Generally, in the image forming apparatus of an electrophotographic type, when a proportion in which an image having a low image ratio (print ratio) is formed is large, a proportion of a toner transferred from a developing sleeve in a developing device onto a photosensitive drum becomes small. In such a state, when the developing device is continuously driven for a long time, toner deterioration generates, and therefore an image defect such as toner scattering or fog is liable to occur. For this reason, an operation in which the toner is forcedly consumed by the developing device has been conventionally performed.
For example, in the case where a value as an index of an amount of the developer used every image formation is smaller than a set reference developer amount, a difference between the value and the set reference developer amount is calculated, and when an integrated value obtained by integrating the calculated difference reaches a predetermined value forced consumption of the toner is executed. Such invention has been proposed (Japanese Laid-Open Patent Application 2006-23327). In the case of the invention described in Japanese Laid-Open Patent Application 2006-23327, the reference developer amount is fixed at a print ratio of 5%.